The present invention relates to azo-compounds useful as dyes, particularly as yellow dyes for polarizing films. The present invention also relates to polarizing films containing the azo-compound.
Polarizing films are produced by causing a polarizing film base, such as a stretch-oriented polyvinyl alcohol film or a polyene film which is produced by dehydrochlorination of a polyvinyl chloride film or dehydration of a polyvinyl alcohol film to form a polyene followed by an orientation of them, to contain iodine or a dichroic dye as a polarizing element. Among them, Iodine-based polarizing films are superior in the early polarizing performance. However, they have problems that they are inferior in durability against heat or water and thus their performance is lowered under high temperature-high humidity conditions In order to improve such durability, a method which include a treatment with an aqueous solution containing formaldehyde or boric acid, a method in which a high molecular film with a low permeability to water vapor is used as a protective film and other methods have been proposed. These methods, however, are not satisfactory.
On the other hand, while dye-based polarizing films in which a dichroic dye is used as a polarizing element are superior in durability against heat and water as compared to iodine polarizing films. However, they are generally inferior in early polarizing performance. Therefore, in order to improve the polarizing performance of dye-based polarizing films, various studies have been conducted on dyes to be used. For example, JP-A-1-172906 describes a polarizing film using a specific azo-compound as a yellow dye. The above polarizing film containing such an azo-compound, however, has not fully met the demands of consumers.
An object of the present invention is to provide yellow compounds suitable for the production of polarizing films having high performance. Another object of the present invention is to provide polarizing Elms with high performance, particularly polarizing films with high performance for liquid crystal projectors, using these compounds.
The present inventors have conducted studies to develop compounds which are good in dyeing ability in the production of polarizing films, which are excellent in polarizing performance and which are excellent in durability and light fastness under high temperature-high humidity conditions, when used as dyes for polarizing films. In addition, they have also conducted studies to develop compounds suitable for dyes which cover a region of comparatively short wavelength of 400 to 500 nm and are used in polarizing films produced by adsorbing two kinds or more of dichroic dyes on a high molecular film and orientating the film. As the result, they have found that specific azo-compounds are suitable for attaining the above objects Thus, the present invention was completed.